Automobile & Light Truck Certification Test A5 BrakesDisc Brake Diagnosis and RepairMedium
A technician is performing a disc brake service and notices that the brake rotor has a small, hairline crack extending from one of the lug stud holes towards the outer edge. The crack is less than 1 inch long. What is the MOST appropriate action?
- AMonitor the crack for growth during the next service interval.
- BReplace the brake rotor immediately.
- CRe-surface the rotor to remove the crack.
- DIgnore the crack, as it is small and not in the friction surface.
Show answer & explanationAnswer & explanation
Correct answer: B. Replace the brake rotor immediately.
Any crack in a brake rotor, regardless of size or location, is a critical safety concern. Cracks can propagate rapidly under braking stresses and heat, leading to rotor failure. The rotor must be replaced immediately.
Why the other options are wrong
- A. Monitoring a crack is unacceptable. It poses an immediate safety risk and could worsen without warning.
- C. Re-surfacing will not remove a crack; it will only make the rotor thinner and potentially weaken it further.
- D. Even small cracks can propagate and lead to catastrophic rotor failure, making this unsafe.
Rotor Cracking
The formation of fissures in a brake rotor, indicating material fatigue or stress.
- Always a critical safety concern.
- Can be caused by excessive heat, thermal shock, or manufacturing defects.
- Requires immediate rotor replacement.
Memory trick: A crack in the shield, a danger revealed.